An Improved Analytical Method For Determining Dynamic Security Region Of Electrical Power Systems Based On Generator's Coherency

The Dynamic Security Region (DSR) of power systems can provide plenty ofsecurity information for stability assessment and control. The fast determination ofDSR found the basis of its wide application. The simulation method determines theDSR reliably but it consumes lots of numerical simulation work, while the analyticalapproach is rapid but the precision of the results needs to be improved.Through the plenty results of simulation method and analytical method, we foundthat the errors of DSR boundary hyper-plane coefficients determined by analyticmethod are correlative highly to generator coherency, and the amplitude of the errorscorresponds to groups of generator coherency. The coherency of the voltage angles ofthe load injection nodes and the errors of DSR boundary hyper-plane coefficientscorrelate also.According to this phenomenon, a new improved analytical method based ongenerator coherency is presented. The generator nodes are divided into several groupsaccording to generator coherency, and the load nodes are divided into groups also bythe coherency of the voltage angles. On the assumption that the nodes'coefficients ofthe analytical method in each group have the same deflection, by adding a few newcritical points, the deflections of the groups are solved through the least-squareapproach.Tests on the IEEE systems show that the improved analytical method reduces theerrors obviously and preserves the speediness feature. Tests on the 10-generator39-bus system show that the error is reduced from about 10% to about 3%.Computation on the 118-bus test system shows that the average error of 500 testpoints is reduced from 5.25% to 0.41%, and the CPU time is about 1% of thesimulation approach.